Pyridine derivatives

ABSTRACT

The present invention relates to compounds of the formula (I) and pharmaceutically acceptable salts and solvates thereof, to processes for the preparation of, intermediates used in the preparation of, and compositions containing such compounds and the uses of such compounds for the treatment of pain.

This application is a 371 application of PCT/IB2005/002214 filed Jul.12, 2005, which claims the benefit of priority to Great Britainprovisional application Serial. No. 416524.7 filed Jul. 23, 2004 andUnited States provisional application Ser. No. 60/646,077 filed Jan. 25,2005.

This invention relates to pyridine derivatives. More particularly, thisinvention relates to 6-amino-2-aminocarbonyl-5-phenyl-pyridinederivatives and to processes for the preparation of, intermediates usedin the preparation of, compositions containing and the uses of, suchderivatives.

The pyridine derivatives of the present invention are sodium channelmodulators and have a number of therapeutic applications, particularlyin the treatment of pain.

More particularly, the pyridine derivatives of the invention areselective Na_(V1.8) modulators. They show an affinity for the Na_(V1.8)channel which is greater than their affinity for thetetrodotoxin-sensitive sodium channels (TTX-S). Preferred pyridinederivatives of the invention show at least a 5-fold selectivity for theNa_(V1.8) channel as compared with the tetrodotoxin-sensitive sodiumchannels.

The Na_(V1.8) channel is a voltage-gated sodium channel which isexpressed in nociceptors, the sensory neurones responsible fortransducing painful stimuli. The rat channel and the human channel havebeen cloned in 1996 and 1998 respectively (Nature 379 (1996), pp.257-262; Pain 1998 November; 78(2):107-14). The Na_(V1.8) channel waspreviously known as SNS (sensory neurone specific) and PN3 (peripheralnerve type 3). The Na_(V1.8) channel is atypical in that it showsresistance to the blocking effects of the puffer fish toxin tetrodotoxinand it is believed to underlie the slow-voltage-gated andtetrodotoxin-resistant (TTX-R) sodium currents recorded from dorsal rootganglion neurones. The closest molecular relative to the Na_(V1.8)channel is the Na_(V1.5) channel, which is the cardiac sodium channel,with which it shares approximately 60% homology. The Na_(V1.8) channelis expressed most highly in the ‘small cells’ of the dorsal root ganglia(DRG). These are thought to be the C- and A-delta cells which are theputative polymodal nociceptors, or pain sensors. Under normalconditions, the Na_(V1.8) channel is not expressed anywhere other thansubpopulations of DRG neurones. The Na_(V1.8) channels are thought tocontribute to the process of DRG sensitisation and also tohyperexcitability due to nerve injury. Inhibitory modulation of theNa_(V1.8) channels is aimed at reducing the excitability of nociceptors,by preventing them from contributing to the excitatory process.

Studies have shown that Na_(V1.8) knock-out leads to a blunted painphenotype, mostly to inflammatory challenges (A. N. Akopian et al., Nat.Neurosci. 2 (1999), 541-548) and that Na_(V1.8) knockdown reduces painbehaviours, in this case neuropathic pain (J. Lai et al., Pain, 2002January; 95(1-2):143-52). Coward et al. and Yiangou et al., have shownthat Na_(V1.8) appears to be expressed in pain conditions (Pain. 2000March; 85(1-2):41-50 and FEBS Lett. 2000 Feb. 11; 467(2-3):249-52).

The Na_(V1.8) channel has also been shown to be expressed in structuresrelating to the back and tooth pulp and there is evidence for a role incausalgia, inflammatory bowel conditions and multiple sclerosis(Bucknill et al., Spine. 2002 Jan. 15; 27(2):135-40: Shembalker et al.,Eur J Pain. 2001; 5(3):319-23: Laird et al., J Neurosci. 2002 Oct. 1;22(19):8352-6: Black et al., Neuroreport. 1999 Apr. 6; 10(5):913-8 andProc. Natl. Acad. Sci. USA 97 (2000), pp. 11598-11602).

Several sodium channel modulators are known for use as anticonvulsantsor antidepressants, such as carbamazepine, amitriptyline, lamotrigineand riluzole, all of which target brain tetradotoxin-sensitive (TTX-S)sodium channels. Such TTX-S agents suffer from dose-limiting sideeffects, including dizziness, ataxia and somnolence, primarily due toaction at TTX-S channels in the brain.

It is an objective of the invention to provide new Na_(V1.8) channelmodulators that are good drug candidates. Preferred compounds shouldbind potently to the Na_(V1.8) channel whilst showing little affinityfor other sodium channels, particularly the TTX-S channels, and showfunctional activity as Na_(V1.8) channel modulators. They should be wellabsorbed from the gastrointestinal tract, be metabolically stable andpossess favourable pharmacokinetic properties. They should be non-toxicand demonstrate few side-effects. Furthermore, the ideal drug candidatewill exist in a physical form that is stable, non-hygroscopic and easilyformulated.

In particular, the pyridine derivatives of the present invention areselective for the Na_(V1.8) channel over the tetradotoxin-sensitive(TTX-S) sodium channels, leading to improvements in the side-effectprofile.

The pyridine derivatives of the present invention are thereforepotentially useful in the treatment of a wide range of disorders,particularly pain, acute pain, chronic pain, neuropathic pain,inflammatory pain, visceral pain, nociceptive pain includingpost-surgical pain, and mixed pain types involving the viscera,gastrointestinal tract, cranial structures, musculoskeletal system,spine, urogenital system, cardiovascular system and CNS, includingcancer pain, back and orofacial pain.

Other conditions that may be treated with the pyridine derivatives ofthe present invention include multiple sclerosis, neurodegenerativedisorders, irritable bowel syndrome, osteoarthritis, rheumatoidarthritis, neuropathological disorders, functional bowel disorders,inflammatory bowel diseases, pain associated with dysmenorrhea, pelvicpain, cystitis, pancreatitis, migraine, cluster and tension headaches,diabetic neuropathy, peripheral neuropathic pain, sciatica, fibromyalgiaand causalgia.

WO-A-96/18616 discloses pyridine derivatives useful as nitric oxidesynthase inhibitors.

6-Amino-N-methyl-5-(2,3,5-trichlorophenyl)nicotinamide has beendisclosed as a modulator of tetrodotoxin-sensitive (TTX-S) sodiumchannels (Gordon Conference, New London, USA, August 2000).

The invention therefore provides a pyridine derivative of the formula(I):

or a pharmaceutically acceptable salt or solvate thereof, whereinR¹ is (C₁-C₆)alkyl optionally substituted with Het¹, Het² or(C₃-C₇)cycloalkyl, wherein said Het¹, Het² and (C₃-C₇)cycloalkyl areoptionally substituted on a ring carbon atom by one or more substituentseach independently selected from (C₁-C₄)alkyl, (C₁-C₄)alkoxy andhalo(C₁-C₄)alkyl;each R² is independently selected from fluoro, chloro, bromo and iodo;n is 1, 2 or 3;Het¹ is a 5- or 6-membered saturated or partially unsaturatedheterocyclic group comprising one or two heteroatom ring members eachindependently selected from nitrogen, oxygen and sulphur, said ringnitrogen atom optionally bearing a (C₁-C₄)alkyl substituent and saidring sulphur atom optionally bearing 1 or 2 oxygen atoms; andHet² is a 5- or 6-membered heteroaryl group comprising either (a) from 1to 4 nitrogen atoms or (b) one oxygen or one sulphur atom and 0, 1 or 2nitrogen atoms.

In the above definitions, halo means fluoro, chloro, bromo or iodo.Alkyl, and alkoxy groups, containing the requisite number of carbonatoms, can be unbranched or branched. Examples of alkyl include methyl,ethyl, n-propyl, i-propyl, n-butyl, i-butyl, sec-butyl and t-butyl.Examples of alkoxy include methoxy, ethoxy, n-propoxy, i-propoxy,n-butoxy, i-butoxy, sec-butoxy and t-butoxy. Examples of cycloalkylinclude cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl andcycloheptyl. Examples of haloalkyl include trifluoromethyl.

Specific examples of Het¹ include tetrahydrofuranyl, pyrrolidinyl,tetrahydropyranyl, piperidinyl, morpholinyl, thiomorpholinyl andpiperazinyl, (optionally substituted as specified above).

Specific examples of Het² include thienyl, furanyl, pyrrolyl, pyrazolyl,imidazolyl, oxazolyl, isoxazolyl, thiazolyl, isothiazolyl, triazolyl,oxadiazolyl, thiadiazolyl, tetrazolyl, pyridinyl, pyridazinyl,pyrimidinyl and pyrazinyl (optionally substituted as specified above).

In a preferred aspect (A), the invention provides a pyridine derivativeof the formula (I), or a pharmaceutically acceptable salt or solvatethereof, wherein R¹ is as defined above, and R² is chloro.

In a preferred aspect (B), the invention provides a pyridine derivativeof the formula (I), or a pharmaceutically acceptable salt or solvatethereof, wherein R² is as defined above, either in its broadest aspector in a preferred aspect under (A) and n is 3; more preferably, the R²groups are in the 2, 3 and 5-positions on the phenyl ring.

In a further preferred aspect (C), the invention provides a pyridinederivative of the formula (I), or a pharmaceutically acceptable salt orsolvate thereof, wherein R² and n are as defined above, either in thebroadest aspect or in a preferred aspect under (A) or (B), and R¹ is(C₁-C₆)alkyl, optionally substituted with piperidinyl, imidazolyl,morpholinyl, piperazinyl or pyrrolidinyl; more preferably R¹ is methyl,ethyl or propyl, optionally substituted with piperidinyl, imidazolyl,morpholinyl, piperazinyl or pyrrolidinyl; most preferably R¹ is methyl.

Individual preferred R¹ groups are methyl; 2-(piperidin-1-yl)ethyl;3-(pyrrolidin-1-yl)propyl; 3-(morpholin-4-yl)propyl;2-(pyrrolidin-1-yl)ethyl; and 3-(imidazol-1-yl)propyl.

Specific preferred pyridine derivatives according to the invention arethose listed below:

-   6-Amino-5-(2,3,5-trichloro-phenyl)-pyridine-2-carboxylic acid    methylamide;-   6-Amino-5-(2,3,5-trichloro-phenyl)-pyridine-2-carboxylic acid    (2-piperidin-1-yl-ethyl)-amide;-   6-Amino-5-(2,3,5-trichloro-phenyl)-pyridine-2-carboxylic acid    (3-pyrrolidin-1-yl-propyl)-amide;-   6-Amino-5-(2,3,5-trichloro-phenyl)-pyridine-2-carboxylic acid    (3-morpholin-4-yl-propyl)-amide;-   6-Amino-5-(2,3,5-trichloro-phenyl)-pyridine-2-carboxylic acid    (2-pyrrolidin-1-yl-ethyl)-amide;-   6-Amino-5-(2,3,5-trichloro-phenyl)-pyridine-2-carboxylic acid    (3-imidazol-1-yl-propyl)-amide; and    the pharmaceutically acceptable salts and solvates thereof.

A particularly preferred pyridine derivative according to the inventionis 6-Amino-5-(2,3,5-trichloro-phenyl)-pyridine-2-carboxylic acidmethylamide or a pharmaceutically acceptable salt or solvate thereof.

The compounds of formula (I), being Na_(V1.8) channel modulators, arepotentially useful in the treatment of a range of disorders. Thetreatment of pain, particularly chronic, inflammatory, neuropathic,nociceptive and visceral pain, is a preferred use.

Physiological pain is an important protective mechanism designed to warnof danger from potentially injurious stimuli from the externalenvironment. The system operates through a specific set of primarysensory neurones and is activated by noxious stimuli via peripheraltransducing mechanisms (see Millan, 1999, Prog. Neurobiol., 57, 1-164for a review). These sensory fibres are known as nociceptors and arecharacteristically small diameter axons with slow conduction velocities.Nociceptors encode the intensity, duration and quality of noxiousstimulus and by virtue of their topographically organised projection tothe spinal cord, the location of the stimulus. The nociceptors are foundon nociceptive nerve fibres of which there are two main types, A-deltafibres (myelinated) and C fibres (non-myelinated). The activitygenerated by nociceptor input is transferred, after complex processingin the dorsal horn, either directly, or via brain stem relay nuclei, tothe ventrobasal thalamus and then on to the cortex, where the sensationof pain is generated.

Pain may generally be classified as acute or chronic. Acute pain beginssuddenly and is short-lived (usually in twelve weeks or less). It isusually associated with a specific cause such as a specific injury andis often sharp and severe. It is the kind of pain that can occur afterspecific injuries resulting from surgery, dental work, a strain or asprain. Acute pain does not generally result in any persistentpsychological response. In contrast, chronic pain is long-term pain,typically persisting for more than three months and leading tosignificant psychological and emotional problems. Common examples ofchronic pain are neuropathic pain (e.g. painful diabetic neuropathy,postherpetic neuralgia), carpal tunnel syndrome, back pain, headache,cancer pain, arthritic pain and chronic post-surgical pain.

When a substantial injury occurs to body tissue, via disease or trauma,the characteristics of nociceptor activation are altered and there issensitisation in the periphery, locally around the injury and centrallywhere the nociceptors terminate. These effects lead to a hightenedsensation of pain. In acute pain these mechanisms can be useful, inpromoting protective behaviours which may better enable repair processesto take place. The normal expectation would be that sensitivity returnsto normal once the injury has healed. However, in many chronic painstates, the hypersensitivity far outlasts the healing process and isoften due to nervous system injury. This injury often leads toabnormalities in sensory nerve fibres associated with maladaptation andaberrant activity (Woolf & Salter, 2000, Science, 288, 1765-1768).

Clinical pain is present when discomfort and abnormal sensitivityfeature among the patient's symptoms. Patients tend to be quiteheterogeneous and may present with various pain symptoms. Such symptomsinclude: 1) spontaneous pain which may be dull, burning, or stabbing; 2)exaggerated pain responses to noxious stimuli (hyperalgesia); and 3)pain produced by normally innocuous stimuli (allodynia—Meyer et al.,1994, Textbook of Pain, 13-44). Although patients suffering from variousforms of acute and chronic pain may have similar symptoms, theunderlying mechanisms may be different and may, therefore, requiredifferent treatment strategies. Pain can also therefore be divided intoa number of different subtypes according to differing pathophysiology,including nociceptive, inflammatory and neuropathic pain.

Nociceptive pain is induced by tissue injury or by intense stimuli withthe potential to cause injury. Pain afferents are activated bytransduction of stimuli by nociceptors at the site of injury andactivate neurons in the spinal cord at the level of their termination.This is then relayed up the spinal tracts to the brain where pain isperceived (Meyer et al., 1994, Textbook of Pain, 13-44). The activationof nociceptors activates two types of afferent nerve fibres. MyelinatedA-delta fibres transmit rapidly and are responsible for sharp andstabbing pain sensations, whilst unmyelinated C fibres transmit at aslower rate and convey a dull or aching pain. Moderate to severe acutenociceptive pain is a prominent feature of pain from central nervoussystem trauma, strains/sprains, burns, myocardial infarction and acutepancreatitis, post-operative pain (pain following any type of surgicalprocedure), posttraumatic pain, renal colic, cancer pain and back pain.Cancer pain may be chronic pain such as tumour related pain (e.g. bonepain, headache, facial pain or visceral pain) or pain associated withcancer therapy (e.g. postchemotherapy syndrome, chronic postsurgicalpain syndrome or post radiation syndrome). Cancer pain may also occur inresponse to chemotherapy, immunotherapy, hormonal therapy orradiotherapy. Back pain may be due to herniated or rupturedintervertebral discs or abnormalities of the lumber facet joints,sacroiliac joints, paraspinal muscles or the posterior longitudinalligament. Back pain may resolve naturally but in some patients, where itlasts over 12 weeks, it becomes a chronic condition which can beparticularly debilitating.

Neuropathic pain is currently defined as pain initiated or caused by aprimary lesion or dysfunction in the nervous system. Nerve damage can becaused by trauma and disease and thus the term ‘neuropathic pain’encompasses many disorders with diverse aetiologies. These include, butare not limited to, peripheral neuropathy, diabetic neuropathy, postherpetic neuralgia, trigeminal neuralgia, back pain, cancer neuropathy,HIV neuropathy, phantom limb pain, carpal tunnel syndrome, centralpost-stroke pain and pain associated with chronic alcoholism,hypothyroidism, uremia, multiple sclerosis, spinal cord injury,Parkinson's disease, epilepsy and vitamin deficiency. Neuropathic painis pathological as it has no protective role. It is often present wellafter the original cause has dissipated, commonly lasting for years,significantly decreasing a patient's quality of life (Woolf and Mannion,1999, Lancet, 353, 1959-1964). The symptoms of neuropathic pain aredifficult to treat, as they are often heterogeneous even betweenpatients with the same disease (Woolf & Decosterd, 1999, Pain Supp., 6,S141-S147; Woolf and Mannion, 1999, Lancet, 353, 1959-1964). Theyinclude spontaneous pain, which can be continuous, and paroxysmal orabnormal evoked pain, such as hyperalgesia (increased sensitivity to anoxious stimulus) and allodynia (sensitivity to a normally innocuousstimulus).

The inflammatory process is a complex series of biochemical and cellularevents, activated in response to tissue injury or the presence offoreign substances, which results in swelling and pain (Levine andTaiwo, 1994, Textbook of Pain, 45-56).

Arthritic pain is the most common inflammatory pain. Rheumatoid diseaseis one of the commonest chronic inflammatory conditions in developedcountries and rheumatoid arthritis is a common cause of disability. Theexact aetiology of rheumatoid arthritis is unknown, but currenthypotheses suggest that both genetic and microbiological factors may beimportant (Grennan & Jayson, 1994, Textbook of Pain, 397-407). It hasbeen estimated that almost 16 million Americans have symptomaticosteoarthritis (OA) or degenerative joint disease, most of whom are over60 years of age, and this is expected to increase to 40 million as theage of the population increases, making this a public health problem ofenormous magnitude (Houge & Mersfelder, 2002, Ann Pharmacother., 36,679-686; McCarthy et al., 1994, Textbook of Pain, 387-395). Mostpatients with osteoarthritis seek medical attention because of theassociated pain. Arthritis has a significant impact on psychosocial andphysical function and is known to be the leading cause of disability inlater life. Ankylosing spondylitis is also a rheumatic disease thatcauses arthritis of the spine and sacroiliac joints. It varies fromintermittent episodes of back pain that occur throughout life to asevere chronic disease that attacks the spine, peripheral joints andother body organs.

Another type of inflammatory pain is visceral pain which includes painassociated with inflammatory bowel disease (IBD). Visceral pain is painassociated with the viscera, which encompass the organs of the abdominalcavity. These organs include the sex organs, spleen and part of thedigestive system. Pain associated with the viscera can be divided intodigestive visceral pain and non-digestive visceral pain. Commonlyencountered gastrointestinal (GI) disorders that cause pain includefunctional bowel disorder (FBD) and inflammatory bowel disease (IBD).These GI disorders include a wide range of disease states that arecurrently only moderately controlled, including, in respect of FBD,gastro-esophageal reflux, dyspepsia, irritable bowel syndrome (IBS) andfunctional abdominal pain syndrome (FAPS), and, in respect of IBD,Crohn's disease, ileitis and ulcerative colitis, all of which regularlyproduce visceral pain. Other types of visceral pain include the painassociated with dysmenorrhea, cystitis and pancreatitis and pelvic pain.

It should be noted that some types of pain have multiple aetiologies andthus can be classified in more than one area, e.g. back pain and cancerpain have both nociceptive and neuropathic components.

Other types of pain include:

-   -   pain resulting from musculo-skeletal disorders, including        myalgia, fibromyalgia, spondylitis, sero-negative        (non-rheumatoid) arthropathies, non-articular rheumatism,        dystrophinopathy, glycogenolysis, polymyositis and pyomyositis;    -   heart and vascular pain, including pain caused by angina,        myocardical infarction, mitral stenosis, pericarditis, Raynaud's        phenomenon, scleredoma and skeletal muscle ischemia;    -   head pain, such as migraine (including migraine with aura and        migraine without aura), cluster headache, tension-type headache        mixed headache and headache associated with vascular disorders;        and    -   orofacial pain, including dental pain, otic pain, burning mouth        syndrome and temporomandibular myofascial pain.

The pyridine derivatives of formula (I) are also expected to be usefulin the treatment of multiple sclerosis.

The invention also relates to therapeutic use of the pyridinederivatives of formula (I) as agents for treating or relieving thesymptoms of neurodegenerative disorders. Such neurodegenerativedisorders include, for example, Alzheimer's disease, Huntington'sdisease, Parkinson's disease, and Amyotrophic Lateral Sclerosis. Thepresent invention also covers treating neurodegenerative disorderstermed acute brain injury. These include but are not limited to: stroke,head trauma, and asphyxia. Stroke refers to a cerebral vascular diseaseand may also be referred to as a cerebral vascular accident (CVA) andincludes acute thromboembolic stroke. Stroke includes both focal andglobal ischemia. Also, included are transient cerebral ischemic attacksand other cerebral vascular problems accompanied by cerebral ischemia.These vascular disorders may occur in a patient undergoing carotidendarterectomy specifically or other cerebrovascular or vascularsurgical procedures in general, or diagnostic vascular proceduresincluding cerebral angiography and the like. Other incidents are headtrauma, spinal cord trauma, or injury from general anoxia, hypoxia,hypoglycemia, hypotension as well as similar injuries seen duringprocedures from embole, hyperfusion, and hypoxia. The instant inventionwould be useful in a range of incidents, for example, during cardiacbypass surgery, in incidents of intracranial hemorrhage, in perinatalasphyxia, in cardiac arrest, and status epilepticus.

A skilled physician will be able to determine the appropriate situationin which subjects are susceptible to or at risk of, for example, strokeas well as suffering from stroke for administration by methods of thepresent invention.

Pharmaceutically acceptable salts of the compounds of formula (I)include the acid addition and base salts thereof.

Suitable acid addition salts are formed from acids which form non-toxicsalts. Examples include the acetate, adipate, aspartate, benzoate,besylate, bicarbonate/carbonate, bisulphate/sulphate, borate, camsylate,citrate, cyclamate, edisylate, esylate, formate, fumarate, gluceptate,gluconate, glucuronate, hexafluorophosphate, hibenzate,hydrochloride/chloride, hydrobromide/bromide, hydroiodide/iodide,isethionate, lactate, malate, maleate, malonate, mesylate,methylsulphate, naphthylate, 2-napsylate, nicotinate, nitrate, orotate,oxalate, palmitate, pamoate, phosphate/hydrogen phosphate/dihydrogenphosphate, pyroglutamate, saccharate, stearate, succinate, tannate,tartrate, tosylate, trifluoroacetate and xinofoate salts.

Suitable base salts are formed from bases which form non-toxic salts.Examples include the aluminium, arginine, benzathine, calcium, choline,diethylamine, diolamine, glycine, lysine, magnesium, meglumine, olamine,potassium, sodium, tromethamine and zinc salts.

Hemisalts of acids and bases may also be formed, for example,hemisulphate and hemicalcium salts.

For a review on suitable salts, see Handbook of Pharmaceutical Salts:Properties, Selection, and Use by Stahl and Wermuth (Wiley-VCH, 2002).

Pharmaceutically acceptable salts of compounds of formula (I) may beprepared by one or more of three methods:

-   (i) by reacting the compound of formula (I) with the desired acid or    base;-   (ii) by removing an acid- or base-labile protecting group from a    suitable precursor of the compound of formula (I) or by ring-opening    a suitable cyclic precursor, for example, a lactone or lactam, using    the desired acid or base; or-   (iii) by converting one salt of the compound of formula (I) to    another by reaction with an appropriate acid or base or by means of    a suitable ion exchange column.

All three reactions are typically carried out in solution. The resultingsalt may precipitate out and be collected by filtration or may berecovered by evaporation of the solvent. The degree of ionisation in theresulting salt may vary from completely ionised to almost non-ionised.

The compounds of the invention may exist in a continuum of solid statesranging from fully amorphous to fully crystalline. The term ‘amorphous’refers to a state in which the material lacks long range order at themolecular level and, depending upon temperature, may exhibit thephysical properties of a solid or a liquid. Typically such materials donot give distinctive X-ray diffraction patterns and, while exhibitingthe properties of a solid, are more formally described as a liquid. Uponheating, a change from solid to liquid properties occurs which ischaracterised by a change of state, typically second order (‘glasstransition’). The term ‘crystalline’ refers to a solid phase in whichthe material has a regular ordered internal structure at the molecularlevel and gives a distinctive X-ray diffraction pattern with definedpeaks. Such materials when heated sufficiently will also exhibit theproperties of a liquid, but the change from solid to liquid ischaracterised by a phase change, typically first order (‘meltingpoint’).

The compounds of the invention may also exist in unsolvated and solvatedforms. The term ‘solvate’ is used herein to describe a molecular complexcomprising the compound of the invention and one or morepharmaceutically acceptable solvent molecules, for example, ethanol. Theterm ‘hydrate’ is employed when said solvent is water.

A currently accepted classification system for organic hydrates is onethat defines isolated site, channel, or metal-ion coordinatedhydrates—see Polymorphism in Pharmaceutical Solids by K. R. Morris (Ed.H. G. Brittain, Marcel Dekker, 1995). Isolated site hydrates are ones inwhich the water molecules are isolated from direct contact with eachother by intervening organic molecules. In channel hydrates, the watermolecules lie in lattice channels where they are next to other watermolecules. In metal-ion coordinated hydrates, the water molecules arebonded to the metal ion.

When the solvent or water is tightly bound, the complex will have awell-defined stoichiometry independent of humidity. When, however, thesolvent or water is weakly bound, as in channel solvates and hygroscopiccompounds, the water/solvent content will be dependent on humidity anddrying conditions. In such cases, non-stoichiometry will be the norm.

Also included within the scope of the invention are multi-componentcomplexes (other than salts and solvates) wherein the drug and at leastone other component are present in stoichiometric or non-stoichiometricamounts. Complexes of this type include clathrates (drug-host inclusioncomplexes) and co-crystals. The latter are typically defined ascrystalline complexes of neutral molecular constituents which are boundtogether through non-covalent interactions, but could also be a complexof a neutral molecule with a salt. Co-crystals may be prepared by meltcrystallisation, by recrystallisation from solvents, or by physicallygrinding the components together—see Chem Commun, 17, 1889-1896, by O.Almarsson and M. J. Zaworotko (2004). For a general review ofmulti-component complexes, see J Pharm Sci, 64 (8), 1269-1288, byHaleblian (August 1975).

The compounds of the invention may also exist in a mesomorphic state(mesophase or liquid crystal) when subjected to suitable conditions. Themesomorphic state is intermediate between the true crystalline state andthe true liquid state (either melt or solution). Mesomorphism arising asthe result of a change in temperature is described as ‘thermotropic’ andthat resulting from the addition of a second component, such as water oranother solvent, is described as ‘lyotropic’. Compounds that have thepotential to form lyotropic mesophases are described as ‘amphiphilic’and consist of molecules which possess an ionic (such as —COO⁻Na⁺,—COO⁻K⁺, or —SO₃ ⁻Na⁺) or non-ionic (such as —N⁻N⁺(CH₃)₃) polar headgroup. For more information, see Crystals and the Polarizing Microscopeby N. H. Hartshorne and A. Stuart, 4^(th) Edition (Edward Arnold, 1970).

Hereinafter all references to compounds of formula I include referencesto salts, solvates; multi-component complexes and liquid crystalsthereof and to solvates, multi-component complexes and liquid crystalsof salts thereof.

The compounds of the invention include compounds of formula (I) ashereinbefore defined, including all polymorphs and crystal habitsthereof, prodrugs and isomers thereof (including optical, geometric andtautomeric isomers) as hereinafter defined and isotopically-labeledcompounds of formula (I).

As indicated, so-called ‘prodrugs’ of the compounds of formula (I) arealso within the scope of the invention. Thus certain derivatives ofcompounds of formula (I) which may have little or no pharmacologicalactivity themselves can, when administered into or onto the body, beconverted into compounds of formula (I) having the desired activity, forexample, by hydrolytic cleavage. Such derivatives are referred to as‘prodrugs’. Further information on the use of prodrugs may be found inPro-drugs as Novel Delivery Systems, Vol. 14, ACS Symposium Series (T.Higuchi and W. Stella) and Bioreversible Carriers in Drug Design,Pergamon Press, 1987 (Ed. E. B. Roche, American PharmaceuticalAssociation).

Prodrugs in accordance with the invention can, for example, be producedby replacing appropriate functionalities present in the compounds offormula (I) with certain moieties known to those skilled in the art as‘pro-moieties’ as described, for example, in Design of Prodrugs by H.Bundgaard (Elsevier, 1985).

Some examples of prodrugs in accordance with the invention include wherethe compound of formula (I) contains a primary or secondary aminofunctionality (—NH₂ or —NHR where R≠H), an amide thereof, for example, acompound wherein, as the case may be, one or both hydrogens of the aminofunctionality of the compound of formula (I) is/are replaced by(C₁-C₁₀)alkanoyl.

Further examples of replacement groups in accordance with the foregoingexamples and examples of other prodrug types may be found in theaforementioned references.

Moreover, certain compounds of formula (I) may themselves act asprodrugs of other compounds of formula (I).

Also included within the scope of the invention are metabolites ofcompounds of formula (I), that is, compounds formed in vivo uponadministration of the drug. Some examples of metabolites in accordancewith the invention include

-   (i) where the compound of formula (I) contains a methyl group, an    hydroxymethyl derivative thereof (—CH₃->—CH₂OH):-   (ii) where the compound of formula (I) contains an alkoxy group, an    hydroxy derivative thereof (—OR->—OH);-   (iii) where the compound of formula (I) contains a secondary amino    group, a primary derivative thereof (—NHR¹->—NH₂);-   (iv) where the compound of formula (I) contains a phenyl moiety, a    phenol derivative thereof (-Ph->-PhOH); and-   (v) where the compound of formula (I) contains an amide group, a    carboxylic acid derivative thereof (—CONH₂->COOH).

Compounds of formula (I) containing one or more asymmetric carbon atomscan exist as two or more stereoisomers. Where a compound of formula (I)contains an alkenyl or alkenylene group, geometric cis/trans (or Z/E)isomers are possible. Where structural isomers are interconvertible viaa low energy barrier, tautomeric isomerism (‘tautomerism’) can occur.This can take the form of proton tautomerism in compounds of formula (I)containing, for example, an imino, keto, or oxime group, or so-calledvalence tautomerism in compounds which contain an aromatic moiety. Itfollows that a single compound may exhibit more than one type ofisomerism.

Included within the scope of the present invention are allstereoisomers, geometric isomers and tautomeric forms of the compoundsof formula (I), including compounds exhibiting more than one type ofisomerism, and mixtures of one or more thereof. Also included are acidaddition or base salts wherein the counterion is optically active, forexample, d-lactate or l-lysine, or racemic, for example, dl-tartrate ordl-arginine.

Cis/trans isomers may be separated by conventional techniques well knownto those skilled in the art, for example, chromatography and fractionalcrystallisation.

Conventional techniques for the preparation/isolation of individualenantiomers include chiral synthesis from a suitable optically pureprecursor or resolution of the racemate (or the racemate of a salt orderivative) using, for example, chiral high pressure liquidchromatography (HPLC).

Alternatively, the racemate (or a racemic precursor) may be reacted witha suitable optically active compound, for example, an alcohol, or, inthe case where the compound of formula (I) contains an acidic or basicmoiety, a base or acid such as 1-phenylethylamine or tartaric acid. Theresulting diastereomeric mixture may be separated by chromatographyand/or fractional crystallization and one or both of thediastereoisomers converted to the corresponding pure enantiomer(s) bymeans well known to a skilled person.

Chiral compounds of the invention (and chiral precursors thereof) may beobtained in enantiomerically-enriched form using chromatography,typically HPLC, on an asymmetric resin with a mobile phase consisting ofa hydrocarbon, typically heptane or hexane, containing from 0 to 50% byvolume of isopropanol, typically from 2% to 20%, and from 0 to 5% byvolume of an alkylamine, typically 0.1% diethylamine. Concentration ofthe eluate affords the enriched mixture.

When any racemate crystallises, crystals of two different types arepossible. The first type is the racemic compound (true racemate)referred to above wherein one homogeneous form of crystal is producedcontaining both enantiomers in equimolar amounts. The second type is theracemic mixture or conglomerate wherein two forms of crystal areproduced in equimolar amounts each comprising a single enantiomer.

While both of the crystal forms present in a racemic mixture haveidentical physical properties, they may have different physicalproperties compared to the true racemate. Racemic mixtures may beseparated by conventional techniques known to those skilled in theart—see, for example, Stereochemistry of Organic Compounds by E. L.Eliel and S. H. Wilen (Wiley, 1994).

The present invention includes all pharmaceutically acceptableisotopically-labelled compounds of formula I wherein one or more atomsare replaced by atoms having the same atomic number, but an atomic massor mass number different from the atomic mass or mass number whichpredominates in nature.

Examples of isotopes suitable for inclusion in the compounds of theinvention include isotopes of hydrogen, such as ²H and ³H, carbon, suchas ¹¹C, ¹³C and ¹⁴C, chlorine, such as ³⁶Cl, fluorine, such as ¹⁸F,iodine, such as ¹²³I and ¹²⁵I, nitrogen, such as ¹³N and ¹⁵N, oxygen,such as ¹⁵O, ¹⁷O and ¹⁸O, phosphorus, such as ³²P, and sulphur, such as³⁵S.

Certain isotopically-labelled compounds of formula (I), for example,those incorporating a radioactive isotope, are useful in drug and/orsubstrate tissue distribution studies. The radioactive isotopes tritium,i.e. ³H, and carbon-14, i.e. ¹⁴C, are particularly useful for thispurpose in view of their ease of incorporation and ready means ofdetection.

Substitution with heavier isotopes such as deuterium, i.e. ²H, mayafford certain therapeutic advantages resulting from greater metabolicstability, for example, increased in vivo half-life or reduced dosagerequirements, and hence may be preferred in some circumstances.

Substitution with positron emitting isotopes, such as ¹¹C, ¹⁸F, ¹⁵O and¹³N, can be useful in Positron Emission Topography (PET) studies forexamining substrate receptor occupancy.

Isotopically-labeled compounds of formula (I) can generally be preparedby conventional techniques known to those skilled in the art or byprocesses analogous to those described in the accompanying Examples andPreparations using an appropriate isotopically-labeled reagent in placeof the non-labeled reagent previously employed.

Pharmaceutically acceptable solvates in accordance with the inventioninclude those wherein the solvent of crystallization may be isotopicallysubstituted, e.g. D₂O, d₆-acetone, d₆-DMSO.

Also within the scope of the invention are intermediate compounds offormulae (V), (VI) and (VII) as defined below, all salts, solvates andcomplexes thereof and all solvates and complexes of salts thereof asdefined hereinbefore for compounds of formula (I). The inventionincludes all polymorphs of the aforementioned species and crystal habitsthereof.

The compounds of formula (I) should be assessed for theirbiopharmaceutical properties, such as solubility and solution stability(across pH), permeability, etc., in order to select the most appropriatedosage form and route of administration for treatment of the proposedindication.

Compounds of the invention intended for pharmaceutical use may beadministered as crystalline or amorphous products. They may be obtainedfor example, as solid plugs, powders, or films by methods such asprecipitation, crystallization, freeze drying, spray drying, orevaporative drying. Microwave or radio frequency drying may be used forthis purpose.

They may be administered alone or in combination with one or more othercompounds of the invention or in combination with one or more otherdrugs (or as any combination thereof). Generally, they will beadministered as a formulation in association with one or morepharmaceutically acceptable excipients. The term ‘excipient’ is usedherein to describe any ingredient other than the compound(s) of theinvention. The choice of excipient will to a large extent depend onfactors such as the particular mode of administration, the effect of theexcipient on solubility and stability, and the nature of the dosageform.

Pharmaceutical compositions suitable for the delivery of compounds ofthe present invention and methods for their preparation will be readilyapparent to those skilled in the art. Such compositions and methods fortheir preparation may be found, for example, in Remington'sPharmaceutical Sciences, 19th Edition (Mack Publishing Company, 1995).

Oral Administration

The compounds of the invention may be administered orally. Oraladministration may involve swallowing, so that the compound enters thegastrointestinal tract, and/or buccal, lingual, or sublingualadministration by which the compound enters the blood stream directlyfrom the mouth.

Formulations suitable for oral administration include solid, semi-solidand liquid systems such as tablets; soft or hard capsules containingmulti- or nano-particulates, liquids, or powders; lozenges (includingliquid-filled); chews; gels; fast dispersing dosage forms; films;ovules; sprays; and buccal/mucoadhesive patches.

Liquid formulations include suspensions, solutions, syrups and elixirs.Such formulations may be employed as fillers in soft or hard capsules(made, for example, from gelatin or hydroxypropylmethylcellulose) andtypically comprise a carrier, for example, water, ethanol, polyethyleneglycol, propylene glycol, methylcellulose, or a suitable oil, and one ormore emulsifying agents and/or suspending agents. Liquid formulationsmay also be prepared by the reconstitution of a solid, for example, froma sachet.

The compounds of the invention may also be used in fast-dissolving,fast-disintegrating dosage forms such as those described in ExpertOpinion in Therapeutic Patents, 11 (6), 981-986, by Liang and Chen(2001).

For tablet dosage forms, depending on dose, the drug may make up from 1weight % to 80 weight % of the dosage form, more typically from 5 weight% to 60 weight % of the dosage form. In addition to the drug, tabletsgenerally contain a disintegrant. Examples of disintegrants includesodium starch glycolate, sodium carboxymethyl cellulose, calciumcarboxymethyl cellulose, croscarmellose sodium, crospovidone,polyvinylpyrrolidone, methyl cellulose, microcrystalline cellulose,lower alkyl-substituted hydroxypropyl cellulose, starch, pregelatinisedstarch and sodium alginate. Generally, the disintegrant will comprisefrom 1 weight % to 25 weight %, preferably from 5 weight % to 20 weight% of the dosage form.

Binders are generally used to impart cohesive qualities to a tabletformulation. Suitable binders include microcrystalline cellulose,gelatin, sugars, polyethylene glycol, natural and synthetic gums,polyvinylpyrrolidone, pregelatinised starch, hydroxypropyl cellulose andhydroxypropyl methylcellulose. Tablets may also contain diluents, suchas lactose (monohydrate, spray-dried monohydrate, anhydrous and thelike), mannitol, xylitol, dextrose, sucrose, sorbitol, microcrystallinecellulose, starch and dibasic calcium phosphate dihydrate.

Tablets may also optionally comprise surface active agents, such assodium lauryl sulfate and polysorbate 80, and glidants such as silicondioxide and talc. When present, surface active agents may comprise from0.2 weight % to 5 weight % of the tablet, and glidants may comprise from0.2 weight % to 1 weight % of the tablet.

Tablets also generally contain lubricants such as magnesium stearate,calcium stearate, zinc stearate, sodium stearyl fumarate, and mixturesof magnesium stearate with sodium lauryl sulphate. Lubricants generallycomprise from 0.25 weight % to 10 weight %, preferably from 0.5 weight %to 3 weight % of the tablet.

Other possible ingredients include anti-oxidants, colourants, flavouringagents, preservatives and taste-masking agents.

Exemplary tablets contain up to about 80% drug, from about 10 weight %to about 90 weight % binder, from about 0 weight % to about 85 weight %diluent, from about 2 weight % to about 10 weight % disintegrant, andfrom about 0.25 weight % to about 10 weight % lubricant.

Tablet blends may be compressed directly or by roller to form tablets.Tablet blends or portions of blends may alternatively be wet-, dry-, ormelt-granulated, melt congealed, or extruded before tabletting. Thefinal formulation may comprise one or more layers and may be coated oruncoated; it may even be encapsulated.

The formulation of tablets is discussed in Pharmaceutical Dosage Forms:Tablets, Vol. 1, by H. Lieberman and L. Lachman (Marcel Dekker, NewYork, 1980).

Consumable oral films for human or veterinary use are typically pliablewater-soluble or water-swellable thin film dosage forms which may berapidly dissolving or mucoadhesive and typically comprise a compound offormula (I), a film-forming polymer, a binder, a solvent, a humectant, aplasticiser, a stabiliser or emulsifier, a viscosity-modifying agent anda solvent. Some components of the formulation may perform more than onefunction.

The compound of formula (I) may be water-soluble or insoluble. Awater-soluble compound typically comprises from 1 weight % to 80 weight%, more typically from 20 weight % to 50 weight %, of the solutes. Lesssoluble compounds may comprise a greater proportion of the composition,typically up to 88 weight % of the solutes. Alternatively, the compoundof formula (I) may be in the form of multiparticulate beads.

The film-forming polymer may be selected from natural polysaccharides,proteins, or synthetic hydrocolloids and is typically present in therange 0.01 to 99 weight %, more typically in the range 30 to 80 weight%.

Other possible ingredients include anti-oxidants, colorants, flavouringsand flavour enhancers, preservatives, salivary stimulating agents,cooling agents, co-solvents (including oils), emollients, bulkingagents, anti-foaming agents, surfactants and taste-masking agents.

Films in accordance with the invention are typically prepared byevaporative drying of thin aqueous films coated onto a peelable backingsupport or paper. This may be done in a drying oven or tunnel, typicallya combined coater dryer, or by freeze-drying or vacuuming.

Solid formulations for oral administration may be formulated to beimmediate and/or modified release. Modified release formulations includedelayed-, sustained-, pulsed-, controlled-, targeted and programmedrelease.

Suitable modified release formulations for the purposes of the inventionare described in U.S. Pat. No. 6,106,864. Details of other suitablerelease technologies such as high energy dispersions and osmotic andcoated particles are to be found in Pharmaceutical Technology On-line,25(2), 1-14, by Verma et al (2001). The use of chewing gum to achievecontrolled release is described in WO 00/35298.

Parenteral Administration

The compounds of the invention may also be administered directly intothe blood stream, into muscle, or into an internal organ. Suitable meansfor parenteral administration include intravenous, intraarterial,intraperitoneal, intrathecal, intraventricular, intraurethral,intrasternal, intracranial, intramuscular, intrasynovial andsubcutaneous. Suitable devices for parenteral administration includeneedle (including microneedle) injectors, needle-free injectors andinfusion techniques.

Parenteral formulations are typically aqueous solutions which maycontain excipients such as salts, carbohydrates and buffering agents(preferably to a pH of from 3 to 9), but, for some applications, theymay be more suitably formulated as a sterile non-aqueous solution or asa dried form to be used in conjunction with a suitable vehicle such assterile, pyrogen-free water.

The preparation of parenteral formulations under sterile conditions, forexample, by lyophilisation, may readily be accomplished using standardpharmaceutical techniques well known to those skilled in the art.

The solubility of compounds of formula (I) used in the preparation ofparenteral solutions may be increased by the use of appropriateformulation techniques, such as the incorporation ofsolubility-enhancing agents.

Formulations for parenteral administration may be formulated to beimmediate and/or modified release. Modified release formulations includedelayed-, sustained-, pulsed-, controlled-, targeted and programmedrelease. Thus compounds of the invention may be formulated as asuspension or as a solid, semi-solid, or thixotropic liquid foradministration as an implanted depot providing modified release of theactive compound. Examples of such formulations include drug-coatedstents and semi-solids and suspensions comprising drug-loadedpoly(dl-lactic-coglycolic)acid (PGLA) microspheres.

Topical Administration

The compounds of the invention may also be administered topically,(intra)dermally, or transdermally to the skin or mucosa. Typicalformulations for this purpose include gels, hydrogels, lotions,solutions, creams, ointments, dusting powders, dressings, foams, films,skin patches, wafers, implants, sponges, fibres, bandages andmicroemulsions. Liposomes may also be used. Typical carriers includealcohol, water, mineral oil, liquid petrolatum, white petrolatum,glycerin, polyethylene glycol and propylene glycol.

Penetration enhancers may be incorporated—see, for example, J Pharm Sci,88 (10), 955-958, by Finnin and Morgan (October 1999).

Other means of topical administration include delivery byelectroporation, iontophoresis, phonophoresis, sonophoresis andmicroneedle or needle-free (e.g. Powderject™, Bioject™, etc.) injection.

Formulations for topical administration may be formulated to beimmediate and/or modified release. Modified release formulations includedelayed-, sustained-, pulsed-, controlled-, targeted and programmedrelease.

Inhaled/Intranasal Administration

The compounds of the invention can also be administered intranasally orby inhalation, typically in the form of a dry powder (either alone, as amixture, for example, in a dry blend with lactose, or as a mixedcomponent particle, for example, mixed with phospholipids, such asphosphatidylcholine) from a dry powder inhaler, as an aerosol spray froma pressurised container, pump, spray, atomiser (preferably an atomiserusing electrohydrodynamics to produce a fine mist), or nebuliser, withor without the use of a suitable propellant, such as1,1,1,2-tetrafluoroethane or 1,1,1,2,3,3,3-heptafluoropropane, or asnasal drops. For intranasal use, the powder may comprise a bioadhesiveagent, for example, chitosan or cyclodextrin.

The pressurised container, pump, spray, atomizer, or nebuliser containsa solution or suspension of the compound(s) of the invention comprising,for example, ethanol, aqueous ethanol, or a suitable alternative agentfor dispersing, solubilising, or extending release of the active, apropellant(s) as solvent and an optional surfactant, such as sorbitantrioleate, oleic acid, or an oligolactic acid.

Prior to use in a dry powder or suspension formulation, the drug productis micronised to a size suitable for delivery by inhalation (typicallyless than 5 microns). This may be achieved by any appropriatecomminuting method, such as spiral jet milling, fluid bed jet milling,supercritical fluid processing to form nanoparticles, high pressurehomogenisation, or spray drying.

Capsules (made, for example, from gelatin orhydroxypropylmethylcellulose), blisters and cartridges for use in aninhaler or insufflator may be formulated to contain a powder mix of thecompound of the invention, a suitable powder base such as lactose orstarch and a performance modifier such as l-leucine, mannitol, ormagnesium stearate. The lactose may be anhydrous or in the form of themonohydrate, preferably the latter. Other suitable excipients includedextran, glucose, maltose, sorbitol, xylitol, fructose, sucrose andtrehalose.

A suitable solution formulation for use in an atomiser usingelectrohydrodynamics to produce a fine mist may contain from 1 μg to 20mg of the compound of the invention per actuation and the actuationvolume may vary from 1 μl to 100 μl. A typical formulation may comprisea compound of formula (I), propylene glycol, sterile water, ethanol andsodium chloride. Alternative solvents which may be used instead ofpropylene glycol include glycerol and polyethylene glycol.

Suitable flavours, such as menthol and levomenthol, or sweeteners, suchas saccharin or saccharin sodium, may be added to those formulations ofthe invention intended for inhaled/intranasal administration.

Formulations for inhaled/intranasal administration may be formulated tobe immediate and/or modified release using, for example, PGLA. Modifiedrelease formulations include delayed-, sustained-, pulsed-, controlled-,targeted and programmed release.

In the case of dry powder inhalers and aerosols, the dosage unit isdetermined by means of a valve which delivers a metered amount. Units inaccordance with the invention are typically arranged to administer ametered dose or “puff” containing from 1 μg to 20 mg of the compound offormula (I). The overall daily dose will typically be in the range 1 μgto 100 mg which may be administered in a single dose or, more usually,as divided doses throughout the day.

Rectal/Intravaginal Administration

The compounds of the invention may be administered rectally orvaginally, for example, in the form of a suppository, pessary, or enema.Cocoa butter is a traditional suppository base, but various alternativesmay be used as appropriate.

Formulations for rectal/vaginal administration may be formulated to beimmediate and/or modified release. Modified release formulations includedelayed-, sustained-, pulsed-, controlled-, targeted and programmedrelease.

Ocular/Aural Administration

The compounds of the invention may also be administered directly to theeye or ear, typically in the form of drops of a micronised suspension orsolution in isotonic, pH-adjusted, sterile saline. Other formulationssuitable for ocular and aural administration include ointments, gels,biodegradable (e.g. absorbable gel sponges, collagen) andnon-biodegradable (e.g. silicone) implants, wafers, lenses andparticulate or vesicular systems, such as niosomes or liposomes. Apolymer such as crossed-linked polyacrylic acid, polyvinylalcohol,hyaluronic acid, a cellulosic polymer, for example,hydroxypropylmethylcellulose, hydroxyethylcellulose, or methylcellulose, or a heteropolysaccharide polymer, for example, gelan gum,may be incorporated together with a preservative, such as benzalkoniumchloride. Such formulations may also be delivered by iontophoresis.

Formulations for ocular/aural administration may be formulated to beimmediate and/or modified release. Modified release formulations includedelayed-, sustained-, pulsed-, controlled-, targeted, or programmedrelease.

Other Technologies

The compounds of the invention may be combined with solublemacromolecular entities, such as cyclodextrin and suitable derivativesthereof or polyethylene glycol-containing polymers, in order to improvetheir solubility, dissolution rate, taste-masking, bioavailabilityand/or stability for use in any of the aforementioned modes ofadministration.

Drug-cyclodextrin complexes, for example, are found to be generallyuseful for most dosage forms and administration routes. Both inclusionand non-inclusion complexes may be used. As an alternative to directcomplexation with the drug, the cyclodextrin may be used as an auxiliaryadditive, i.e. as a carrier, diluent, or solubiliser. Most commonly usedfor these purposes are alpha-, beta- and gamma-cyclodextrins, examplesof which may be found in International Patent Applications Nos. WO91/11172, WO 94/02518 and WO 98/55148.

Kit-of-Parts

Inasmuch as it may desirable to administer a combination of activecompounds, for example, for the purpose of treating a particular diseaseor condition, it is within the scope of the present invention that twoor more pharmaceutical compositions, at least one of which contains acompound in accordance with the invention, may conveniently be combinedin the form of a kit suitable for coadministration of the compositions.

Thus the kit of the invention comprises two or more separatepharmaceutical compositions, at least one of which contains a compoundof formula (I) in accordance with the invention, and means forseparately retaining said compositions, such as a container, dividedbottle, or divided foil packet. An example of such a kit is the familiarblister pack used for the packaging of tablets, capsules and the like.

The kit of the invention is particularly suitable for administeringdifferent dosage forms, for example, oral and parenteral, foradministering the separate compositions at different dosage intervals,or for titrating the separate compositions against one another. Toassist compliance, the kit typically comprises directions foradministration and may be provided with a so-called memory aid.

Dosage

For administration to human patients, the total daily dose of thecompounds of the invention is typically in the range 0.1 mg to 1000 mgdepending, of course, on the mode of administration. For example, oraladministration may require a total daily dose of from 1 mg to 1000 mg,while an intravenous dose may only require from 0.1 mg to 100 mg. Thetotal daily dose may be administered in single or divided doses and may,at the physician's discretion, fall outside of the typical range givenherein.

These dosages are based on an average human subject having a weight ofabout 60 kg to 70 kg. The physician will readily be able to determinedoses for subjects whose weight falls outside this range, such asinfants and the elderly.

For the avoidance of doubt, references herein to “treatment” includereferences to curative, palliative and prophylactic treatment.

A Na_(V1.8) channel modulator may be usefully combined with anotherpharmacologically active compound, or with two or more otherpharmacologically active compounds, particularly in the treatment ofpain. For example, a Na_(V1.8) channel modulator, particularly acompound of formula (I), or a pharmaceutically acceptable salt orsolvate thereof, as defined above, may be administered simultaneously,sequentially or separately in combination with one or more agentsselected from:

-   -   an opioid analgesic, e.g. morphine, heroin, hydromorphone,        oxymorphone, levorphanol, levallorphan, methadone, meperidine,        fentanyl, cocaine, codeine, dihydrocodeine, oxycodone,        hydrocodone, propoxyphene, nalmefene, nalorphine, naloxone,        naltrexone, buprenorphine, butorphanol, nalbuphine or        pentazocine;    -   a nonsteroidal antiinflammatory drug (NSAID), e.g. aspirin,        diclofenac, diflusinal, etodolac, fenbufen, fenoprofen,        flufenisal, flurbiprofen, ibuprofen, indomethacin, ketoprofen,        ketorolac, meclofenamic acid, mefenamic acid, meloxicam,        nabumetone, naproxen, nimesulide, nitroflurbiprofen, olsalazine,        oxaprozin, phenylbutazone, piroxicam, sulfasalazine, sulindac,        tolmetin or zomepirac;    -   a barbiturate sedative, e.g. amobarbital, aprobarbital,        butabarbital, butabital, mephobarbital, metharbital,        methohexital, pentobarbital, phenobartital, secobarbital,        talbutal, theamylal or thiopental;    -   a benzodiazepine having a sedative action, e.g.        chlordiazepoxide, clorazepate, diazepam, flurazepam, lorazepam,        oxazepam, temazepam or triazolam;    -   an H₁ antagonist having a sedative action, e.g.        dipherihydramine, pyrilamine, promethazine, chlorpheniramine or        chlorcyclizine;    -   a sedative such as glutethimide, meprobamate, methaqualone or        dichloralphenazone;    -   a skeletal muscle relaxant, e.g. baclofen, carisoprodol,        chlorzoxazone, cyclobenzaprine, methocarbamol or orphrenadine;    -   an NMDA receptor antagonist, e.g. dextromethorphan        ((+)-3-hydroxy-N-methylmorphinan) or its metabolite dextrorphan        ((+)-3-hydroxy-N-methylmorphinan), ketamine, memantine,        pyrroloquinoline quinine,        cis-4-(phosphonomethyl)-2-piperidinecarboxylic acid, budipine,        EN-3231 (MorphiDex®, a combination formulation of morphine and        dextromethorphan), topiramate, neramexane or perzinfotel        including an NR2B antagonist, e.g. ifenprodil, traxoprodil or        (−)-(R)-6-(2-[4-(3-fluorophenyl)-4-hydroxy-1-piperidinyl]-1-hydroxyethyl-3,4-dihydro-2(1H)-quinolinone;    -   an alpha-adrenergic, e.g. doxazosin, tamsulosin, clonidine,        guanfacine, dexmetatomidine, modafinil, or        4-amino-6,7-dimethoxy-2-(5-methane-sulfonamido-1,2,3,4-tetrahydroisoquinol-2-yl)-5-(2-pyridyl)        quinazoline;    -   a tricyclic antidepressant, e.g. desipramine, imipramine,        amitriptyline or nortriptyline;    -   an anticonvulsant, e.g. carbamazepine, lamotrigine, topiratmate        or valproate;    -   a tachykinin (NK) antagonist, particularly an NK-3, NK-2 or NK-1        antagonist, e.g.        (αR,9R)-7-[3,5-bis(trifluoromethyl)benzyl]-8,9,10,11-tetrahydro-9-methyl-5-(4-methylphenyl)-7H-[1,4]diazocino[2,1-g][1,7]-naphthyridine-6-13-dione        (TAK-637),        5-[[(2R,3S)-2-[(1R)-1-[3,5-bis(trifluoromethyl)phenyl]ethoxy-3-(4-fluorophenyl)-4-morpholinyl]-methyl]-1,2-dihydro-3H-1,2,4-triazol-3-one        (MK-869), aprepitant, lanepitant, dapitant or        3-[[2-methoxy-5-(trifluoromethoxy)phenyl]-methylamino]-2-phenylpiperidine        (2S,3S);    -   a muscarinic antagonist, e.g oxybutynin, tolterodine,        propiverine, tropsium chloride, darifenacin, solifenacin,        temiverine and ipratropium;    -   a COX-2 selective inhibitor, e.g. celecoxib, rofecoxib,        parecoxib, valdecoxib, deracoxib, etoricoxib, or lumiracoxib;    -   a coal-tar analgesic, in particular paracetamol;    -   a neuroleptic such as droperidol, chlorpromazine, haloperidol,        perphenazine, thioridazine, mesoridazine, trifluoperazine,        fluphenazine, clozapine, olanzapine, risperidone, ziprasidone,        quetiapine, sertindole, aripiprazole, sonepiprazole,        blonanserin, iloperidone, perospirone, raclopride, zotepine,        bifeprunox, asenapine, lurasidone, amisulpride, balaperidone,        palindore, eplivanserin, osanetant, rimonabant, meclinertant,        Miraxion® or sarizotan;    -   a vanilloid receptor agonist (e.g. resinferatoxin) or antagonist        (e.g. capsazepine);    -   a beta-adrenergic such as propranolol;    -   a local anaesthetic such as mexiletine;    -   a corticosteroid such as dexamethasone;    -   a 5-HT receptor agonist or antagonist, particularly a        5-HT_(1B/1D) agonist such as eletriptan, sumatriptan,        naratriptan, zolmitriptan or rizatriptan;    -   a 5-HT_(2A) receptor antagonist such as        R(+)-alpha-(2,3-dimethoxy-phenyl)-1-[2-(4-fluorophenylethyl)]-4-piperidinemethanol        (MDL-100907);    -   a cholinergic (nicotinic) analgesic, such as ispronicline        (TC-1734), (E)-N-methyl-4-(3-pyridinyl)-3-buten-1-amine        (RJR-2403), (R)-5-(2-azetidinylmethoxy)-2-chloropyridine        (ABT-594) or nicotine;    -   Tramadol®;    -   a PDEV inhibitor, such as        5-[2-ethoxy-5-(4-methyl-1-piperazinyl-sulphonyl)phenyl]-1-methyl-3-n-propyl-1,6-dihydro-7H-pyrazolo[4,3-d]pyrimidin-7-one        (sildenafil),        (6R,12aR)-2,3,6,7,12,12a-hexahydro-2-methyl-6-(3,4-methylenedioxyphenyl)-pyrazino[2′,1′:6,1]-pyrido[3,4-b]indole-1,4-dione        (IC-351 or tadalafil),        2-[2-ethoxy-5-(4-ethyl-piperazin-1-yl-1-sulphonyl)-phenyl]-5-methyl-7-propyl-3H-imidazo[5,1-f][1,2,4]triazin-4-one        (vardenafil),        5-(5-acetyl-2-butoxy-3-pyridinyl)-3-ethyl-2-(1-ethyl-3-azetidinyl)-2,6-dihydro-7H-pyrazolo[4,3-d]pyrimidin-7-one,        5-(5-acetyl-2-propoxy-3-pyridinyl)-3-ethyl-2-(1-isopropyl-3-azetidinyl)-2,6-dihydro-7H-pyrazolo[4,3-d]pyrimidin-7-one,        5-[2-ethoxy-5-(4-ethylpiperazin-1-ylsulphonyl)pyridin-3-yl]-3-ethyl-2-[2-methoxyethyl]-2,6-dihydro-7H-pyrazolo[4,3-d]pyrimidin-7-one,        4-[(3-chloro-4-methoxybenzyl)amino]-2-[(2S)-2-(hydroxymethyl)pyrrolidin-1-yl]-N-(pyrimidin-2-ylmethyl)pyrimidine-5-carboxamide,        3-(1-methyl-7-oxo-3-propyl-6,7-dihydro-1H-pyrazolo[4,3-d]pyrimidin-5-yl)-N-[2-(1-methylpyrrolidin-2-yl)ethyl]-4-propoxybenzenesulfonamide;    -   an alpha-2-delta ligand such as gabapentin, pregabalin,        3-methylgabapentin,        (1α,3α,5α)(3-amino-methyl-bicyclo[3.2.0]hept-3-yl)-acetic acid,        (3S,5R)-3-aminomethyl-5-methyl-heptanoic acid,        (3S,5R)-3-amino-5-methyl-heptanoic acid,        (3S,5R)-3-amino-5-methyl-octanoic acid,        (2S,4S)-4-(3-chlorophenoxy)proline,        (2S,4S)-4-(3-fluorobenzyl)-proline,        [(1R,5R,6S)-6-(aminomethyl)bicyclo[3.2.0]hept-6-yl]acetic acid,        3-(1-aminomethyl-cyclohexylmethyl)-4H-[1,2,4]oxadiazol-5-one,        C-[1-(1H-tetrazol-5-ylmethyl)-cycloheptyl]-methylamine,        (3S,4S)-(1-aminomethyl-3,4-dimethyl-cyclopentyl)-acetic acid,        (3S,5R)-3-aminomethyl-5-methyl-octanoic acid,        (3S,5R)-3-amino-5-methyl-nonanoic acid,        (3S,5R)-3-amino-5-methyl-octanoic acid,        (3R,4R,5R)-3-amino-4,5-dimethyl-heptanoic acid and        (3R,4R,5R)-3-amino-4,5-dimethyl-octanoic acid;    -   a cannabinoid;    -   metabotropic glutamale subtype 1 receptor (mGluR1) antagonist;    -   a serotonin reuptake inhibitor such as sertraline, sertraline        metabolite demethylsertraline, fluoxetine, norfluoxetine        (fluoxetine desmethyl metabolite), fluvoxamine, paroxetine,        citalopram, citalopram metabolite desmethylcitalopram,        escitalopram, d,l-fenfluramine, femoxetine, ifoxetine,        cyanodothiepin, litoxetine, dapoxetine, nefazodone, cericlamine        and trazodone;    -   a noradrenaline (norepinephrine) reuptake inhibitor, such as        maprotiline, lofepramine, mirtazepine, oxaprotiline, fezolamine,        tomoxetine, mianserin, buproprion, buproprion metabolite        hydroxybuproprion, nomifensine and viloxazine (Vivalan®),        especially a selective noradrenaline reuptake inhibitor such as        reboxetine, in particular (S,S)-reboxetine;    -   a dual serotonin-noradrenaline reuptake inhibitor, such as        venlafaxine, venlafaxine metabolite O-desmethylvenlafaxine,        clomipramine, clomipramine metabolite desmethylclomipramine,        duloxetine, milnacipran and imipramine;    -   an inducible nitric oxide synthase (iNOS) inhibitor such as        S-[2-[(1-iminoethyl)amino]ethyl]-L-homocysteine,        S-[2-[(1-iminoethyl)-amino]ethyl]-4,4-dioxo-L-cysteine,        S-[2-[(1-iminoethyl)amino]ethyl]-2-methyl-L-cysteine,        (2S,5Z)-2-amino-2-methyl-7-[(1-iminoethyl)amino]-5-heptenoic        acid,        2-[[(1R,3S)-3-amino-4-hydroxy-1-(5-thiazolyl)-butyl]thio]-5-chloro-3-pyridinecarbonitrile;        2-[[(1R,3S)-3-amino-4-hydroxy-1-(5-thiazolyl)butyl]thio]-4-chlorobenzonitrile,        (2S,4R)-2-amino-4-[[2-chloro-5-(trifluoromethyl)phenyl]thio]-5-thiazolebutanol,        2-[[(1R,3S)-3-amino-4-hydroxy-1-(5-thiazolyl)butyl]thio]-6-(trifluoromethyl)-3        pyridinecarbonitrile,        2-[[(1R,3S)-3-amino-4-hydroxy-1-(5-thiazolyl)butyl]thio]-5-chlorobenzonitrile,        N-[4-[2-(3-chlorobenzylamino)ethyl]phenyl]thiophene-2-carboxamidine,        or guanidinoethyldisulfide;    -   an acetylcholinesterase inhibitor such as donepezil;    -   a prostaglandin E₂ subtype 4 (EP4) antagonist such as        N-[({2-[4-(2-ethyl-4,6-dimethyl-1H-imidazo[4,5-c]pyridin-1-yl)phenyl]ethyl}amino)-carbonyl]-4-methylbenzenesulfonamide        or        4-[(1S)-1-({[5-chloro-2-(3-fluorophenoxy)pyridin-3-yl]carbonyl}amino)ethyl]benzoic        acid;    -   a leukotriene B4 antagonist; such as        1-(3-biphenyl-4-ylmethyl-4-hydroxy-chroman-7-yl)-cyclopentanecarboxylic        acid (CP-105696),        5-[2-(2-Carboxyethyl)-3-[6-(4-methoxyphenyl)-5E-hexenyl]oxyphenoxy]-valeric        acid (ONO-4057) or DPC-11870,    -   a 5-lipoxygenase inhibitor, such as zileuton,        6-[(3-fluoro-5-[4-methoxy-3,4,5,6-tetrahydro-2H-pyran-4-yl])phenoxy-methyl]-1-methyl-2-quinolone        (ZD-2138), or 2,3,5-trimethyl-6-(3-pyridylmethyl),        1,4-benzoquinone (CV-6504);    -   a sodium channel blocker, such as lidocaine;    -   a 5-HT3 antagonist, such as ondansetron;        and the pharmaceutically acceptable salts and solvates thereof.

Such combinations offer significant advantages, including synergisticactivity, in therapy.

The ability of the pyridine derivatives of the formula (I) to inhibitthe Na_(V1.8) channel may be measured using the assay described below.

VIPR Assay for Nav1.8 Compounds

This screen is used to determine the effects of compounds ontetrodotoxin-resistant (TTX-R) sodium channels in Human Nav1.8 (HEK293)expressing cell line, utilising the technology of Aurora's fluorescentVoltage/Ion Probe Reader (VIPR). This experiment is based on FRET(Fluorescence Resonance Energy Transfer) and uses two fluorescentmolecules. The first molecule, Oxonol (DiSBAC₂(3)), is a highlyfluorescent, negatively charged, hydrophobic ion that “senses” thetrans-membrane electrical potential. In response to changes in membranepotential, it can rapidly redistribute between two binding sites onopposite sides of the plasma membrane. The voltage dependentredistribution is transduced into a ratiometric fluorescent readout viaa second fluorescent molecule (Coumarin (CC2-DMPE)) that bindsspecifically to one face of the plasma membrane and functions as a FRETpartner to the mobile voltage-sensing ion. To enable the assay to work,the channels have to be pharmacologically held in the open state. Thisis achieved by treating the cells with either deltamethrin (forNa_(V1.8)) or veratridine (for the SHSY-5Y assay for TTX-S channels).

Cell Maintenance:

Human Nav1.8 cells were grown in T225 flasks, in a 5% CO2 humidifiedincubator to about 70% confluence. Media composition consisted ofDMEM/F-12, 10% FCS and 300 μg/ml Geneticine. They were split using celldissociation fluid 1:5 to 1:20, depending on scheduling needs, and grownfor 3-4 days before the next split.

Protocol:

Day One:

Plate-out HEK-Nav1.8 cells (100 μl per well) into poly-D-lysine coatedplates prior to experimentation as follows:—24 hours @ 3.5×10⁴cells/well (3.5×10⁵ cells/ml) or using the technology of Select.

Day Two: VIPR Assay:

1. Equilibrate buffers at room temperature for 2 hours or at 37° C. for30 minutes prior to experimentation.

2. Prepare Coumarin dye (see below) and store in dark. Prime with theplate washer with Na⁺ Free buffer and wash cells twice, Note: Platewasher deposits ˜30111 residual buffer per well. Add 100 μL Coumarin(CC2-DMPE) solution (see appendix) to cells and incubate for 45 minutesat room temperature avoiding bright light.3. Prepare Oxonol (DiSBAC₂(3)) dye (see below):4. Aspirate off Coumarin solution from the cells by washing in Na+ Freebuffer.5. Add 30 μl compound (refer to addition plates). Add 30 μl Oxonolsolution to the cells and incubate for 45 minutes at room temperature inthe dark (total well volume ˜90 μl).6. Once the incubation is complete, the cells are ready to be assayedusing the VIPR for sodium addback membrane potential.

The data was analyzed and reported as normalised ratios of intensitiesmeasured in the 460 nm and 580 nm channels. The process of calculatingthese ratios was performed as follows. An additional plate containedcontrol solution with the same DisBAC2(3) concentrations as used in thecell plates, however no cells were included in the background plate.Intensity values at each wavelength were averaged for sample points 5-7(initial) and 44-49 (final). These averages were subtracted fromintensity values averaged over the same time periods in all assay wells.The initial ratio obtained from samples 3-8 (Ri) and the final ratioobtained from samples 45-50 (Rf) are defined as:

$\begin{matrix}{{Ri} = \frac{\left( {{{Intensity}\mspace{14mu} 460\mspace{14mu}{nm}},{{{samples}\mspace{14mu} 3\text{-}5} - {{background}\mspace{14mu} 460\mspace{14mu}{nm}}},{{samples}\mspace{14mu} 3\text{-}5}} \right)}{\left( {{{Intensity}\mspace{14mu} 580\mspace{14mu}{nm}},{{{samples}\mspace{14mu} 3\text{-}5} - {{background}\mspace{14mu} 580\mspace{14mu}{nm}}},{{samples}\mspace{14mu} 3\text{-}5}} \right)}} \\{{Rf} = \frac{\begin{pmatrix}{{{Intensity}\mspace{14mu} 460\mspace{14mu}{nm}},{{{samples}\mspace{14mu} 25\text{-}30} -}} \\{{{background}\mspace{14mu} 460\mspace{14mu}{nm}},{{samples}\mspace{14mu} 25\text{-}30}}\end{pmatrix}}{\begin{pmatrix}{{{Intensity}\mspace{14mu} 580\mspace{14mu}{nm}},{{{samples}\mspace{14mu} 25\text{-}30} -}} \\{{{background}\mspace{14mu} 580\mspace{14mu}{nm}},{{samples}\mspace{14mu} 25\text{-}30}}\end{pmatrix}}}\end{matrix}$

Final data are normalised to the starting ratio of each well andreported as Rf/Ri. This analysis is performed using a computerisedspecific programme designed for VIPR generated data.

Rf/Ri ratio values are plotted using Excel Labstats (curve fit) oranalysed via ECADA to determine an IC50 value for each compound.

weight/ 10X Conc. 1X Conc. Component: Mwt/Conc^(n): volume (mM) (mM):Na+-Addback Buffer pH 7.4 (adjust with 5M NaOH) - 10X stock NaCl 58.4493.5 g 1600 160 KCL 74.55 3.35 g 45.0 4.5 CaCl2 1M solution 20 ml 20.0 2MgCl2 203.31 2.03 g 10.0 1 Hepes 238.3 23.83 g 100 10 dH2O 1 L Na+-FreeBuffer pH 7.4 (adjust with 5M KOH) - 10X stock Choline 139.6 223.36 g1600 160 CaCl2 1M solution 1 ml 1.0 0.1 MgCl2 203.31 2.03 g 10.0 1.0Hepes 238.3 23.83 g 100 10 dH2O 1 L Coumarin (CC2-DMPE): For 2 plates: -First mix 220 μl Coumarin (1 mM) + 22 μl Pluronic (20%) in a tube +22 ml1X Na+-Free Buffer, gently vortex. Solution Conc^(n): Final AssayConc^(n) Coumarin (1 mM) 10 μM 10 μM Oxonol (DiSBAC₂(3)): For 2plates: - 48 μl Oxonol (5 mM) + 120 ul Tartrazine (200 mM) Vortex 8.0 ml2X Na+-Free Buffer Vortex 1.6 μl Deltametherin (5 mM) Vortex SolutionConc^(n): Final Assay Conc^(n) Oxonol (5 mM) 30 μM 10 μM Deltametherin(5 mM) 1 μM 330 nM Tartrazine (200 mM) 3 mM 1.0 mM 1X Na+ Free Buffer: -400 ml 10X + 3600 ml dH2O 2X Na+ Free Buffer: - 100 ml 10X + 400 ml dH2O1X Na+ Addback Buffer: - 50 ml 10X Na+ Addback + 450 ml dH2OTTX-S Assay

The TTX-S assay was performed in the native SHSY-5Y cell line. Thesecells express a number of tetrodotoxin-sensitive voltage-gated sodiumchannels including Na_(V1.2), Na_(V1.3) and Na_(V1.7). The proceduredetailed above for the Na_(V1.8) assay was followed with the exceptionthat veratridine was substituted for deltamethrin in the assay as anopener of the sodium channels, at a final assay concentration of 50 μM.

All of the pyridine derivatives of the formula (I) can be prepared bythe procedures described in the general methods presented below or bythe specific methods described in the Examples section and thePreparations section, or by routine modifications thereof. The presentinvention also encompasses any one or more of these processes forpreparing the pyridine derivatives of formula (I), in addition to anynovel intermediates used therein.

In the following general methods, R¹, R² and n are as previously definedfor a pyridine derivative of the formula (I) unless otherwise stated.

According to a first process, pyridine derivatives of formula (I) may beprepared from compounds of formulae (VI) or (VII), as illustrated byScheme1.

wherein X is a suitable leaving group, such as trifluoromethanesulfonyl,fluoro, chloro, bromo, iodo;PG is a suitable protecting group, such as tert-butoxycarbonyl,N-benzyloxycarbonyl, tert-butylcarbonyl or methylcarbonyl;R³ is a suitable ester group such as (C₁-C₆)alkyl, benzyl;M is hydrogen or an alkali metal; andM¹ is a suitable coupling group such as a stannane, borane or boronicacid, metal or metalhalide.

Compounds of formula (III) can be prepared from compounds of formula(II) by reaction with a suitable acid chloride or anhydride, optionallyin the presence of an acid acceptor, in a suitable solvent such asdichloromethane or dioxan, at a temperature of from 25 to 50° C. for5-18 hours. PG is suitably tert-butoxycarbonyl, N-benzyloxycarbonyl,tert-butylcarbonyl or methylcarbonyl, preferably tert-butylcarbonyl ormethylcarbonyl, and most preferably methylcarbonyl.

When PG is methylcarbonyl, typical conditions are analogous to thosedescribed in Bioorg. Med. Chem. 9, 2061-2071, 2001 and comprise of 1.0equivalent of compound (II) and an excess of acetic anhydride in dioxan,at 50° C. for 18 hours.

Compounds of formula (IV) can be prepared from compounds of formula(III) by oxidation with a suitable oxidising agent, such as potassiumpermanganate or sodium dichromate, in a suitable solvent, such as wateror water with pyridine, at a temperature of from 65 to 75° C. for 3-18hours. Typical conditions comprise 1.0 equivalent of compound (III) and2.0-6.0 equivalents of potassium permanganate, in a mixture of water andpyridine, at 75° C. for 18 hours.

Compounds of formula (V) can be prepared either as described in J. Org.Chem. 61, 4623-4633, 1996 or from compounds of formula (IV) byalkylation with a suitable alcohol in the presence of a suitable acid,such as concentrated hydrochloric acid or concentrated sulfuric acid,heated under reflux for 18-72 hours. Removal of the amine protectinggroup (PG) occurs concomitantly under these conditions. Typicalconditions comprise of 1.0 equivalent of compound (IV) and an excess ofmethanol, in the presence of concentrated sulfuric acid, heated underreflux for 48 hours.

Alternatively, compounds of general formula (V) can be prepared fromcompounds of general formula (III) by combination of steps ii and iii.Typical conditions comprise of 1.0 equivalent of compound (III) and2.0-6.0 equivalents of potassium permanganate, in a mixture of water andpyridine, at 75° C. for 18 hours. Concentration in vacuo is followed byaddition of methanol and concentrated sulfuric acid, heated under refluxfor 48 hours to yield the desired product.

Compounds of formula (VI) can be prepared by reaction of compounds offormula (V) with an amine, NH₂R¹, in a suitable solvent, such asdichloromethane or a mixture of tetrahydrofuran/R³OH, at a temperatureof from 25° C. to reflux, for 18-72 hours. Typical conditions compriseof 1.0 equivalent of compound (V) and 5.0-10.0 equivalents of NH₂R¹ intetrahydrofuran/methanol, at 25-80° C. for 18-72 hours.

Alternatively, this reaction can also be carried out at elevatedtemperature using a microwave. Typical conditions comprise of 1.0equivalent of compound (V) and 5.0-10.0 equivalents of NH₂R¹ intetrahydrofuran/methanol, at 130° C. for 30 minutes, followed bystirring at room temperature for 72 hours.

Compounds of formula (VII) can be prepared from compounds of formula (V)by a cross-coupling reaction with a compound of formula (VIII), where M¹is suitably trialkyl stannane, dihydroxy borane, dialkoxy borane,lithium, halomagnesium, or halozinc, and preferably dihydroxy borane, inthe presence of an appropriate catalyst system (e.g. a palladium ornickel catalyst) and an excess of a suitable base, such as potassiumcarbonate, potassium fluoride or triethylamine, in a suitable solventsuch as dioxan or tetrahydrofuran, at a temperature of from 25° C. toreflux, for 1-18 hours. Typical conditions comprise of 1.0 equivalent ofcompound (V), 1.0-1.1 equivalents of a suitable boronic acid such asbenzeneboronic acid or 2,3,5-trichlorobenzeneboronic acid, 3.2-3.3equivalents of potassium fluoride, tris(dibenzylideneacetone)dipalladium(0) (catalytic), and bis(tri-tert-butylphosphine)palladium(0) (catalytic) in tetrahydrofuran, under ambient conditionsfor 18 hours.

Those skilled in the art will appreciate that the type of catalyst thatis employed will depend on factors such as the nature of the M¹ group,the substrate employed etc. Examples of such coupling reactions includethe so-called “Suzuki” conditions, “Stille” conditions or “Negishi”conditions as described in “Metal Catalysed cross-coupling reactions”,edited by F. Diederich, Wiley-VCH 1998 and references therein.

A pyridine derivative of formula (I) may be prepared from a compound offormula (VI) by a cross-coupling reaction with a compound of formula(VIII). The reaction conditions are as described above for process stepv.

Alternatively, a pyridine derivative of formula (I) may be prepared byreaction of a compound of formula (VII) with an amine, NH₂R¹. Thereaction conditions are as described above for process step iv.

Referring to the general methods above, it will be readily understood tothe skilled person that where protecting groups are present, these willbe generally interchangeable with other protecting groups of a similarnature, e.g. where an amine is described as being protected with atert-butoxycarbonyl group, this may be readily interchanged with anysuitable amine protecting group. Suitable protecting groups aredescribed in ‘Protective Groups in Organic Synthesis’ by T. Greene andP. Wuts (3^(rd) edition, 1999, John Wiley and Sons).

The present invention also relates to novel intermediate compounds offormulae (V), (VI) and (VII) as defined above, all salts, solvates andcomplexes thereof and all solvates and complexes of salts thereof asdefined hereinbefore for pyridine derivatives of formula (I). Theinvention includes all polymorphs of the aforementioned species andcrystal habits thereof.

When preparing pyridine derivatives of formula (I) in accordance withthe invention, it is open to a person skilled in the art to routinelyselect the form of compound of formulae (V), (VI) or (VII) whichprovides the best combination of features for this purpose. Suchfeatures include the melting point, solubility, processability and yieldof the intermediate form and the resulting ease with which the productmay be purified on isolation.

The following Examples illustrate the preparation of pyridinederivatives of the formula (I).

EXAMPLE 1 6-Amino-5-(2,3,5-trichloro-phenyl)-pyridine-2-carboxylic acidmethylamide

A solution of bis(tri-tert-butylphosphine)palladium(0) (135 mg, 0.27mmol) in tetrahydrofuran (11 mL) was added to a mixture of the productof preparation 4 (1.36 g, 5.92 mmol), potassium fluoride (1.14 g, 19.55mmol), 2,3,5-trichlorobenzeneboronic acid (1.46 g, 6.51 mmol) andtris(dibenzylideneacetone)dipalladium(0) (81 mg, 0.09 mmol) intetrahydrofuran (27 mL) and the reaction mixture was stirred undernitrogen for 18 hours at room temperature. The mixture was then filteredthrough Arbocel® and washed with tetrahydrofuran. The filtrate wasconcentrated in vacuo and purified by column chromatography on silicagel, eluting with heptane:ethyl acetate, 50:50, to afford the titlecompound as a white solid in 80% yield, 1.57 g.

¹H NMR (400 MHz, CD₃OD) δ: 2.94 (s, 3H), 7.33 (d, 1H), 7.41 (dd, 2H),7.68 (d, 1H)

LRMS: m/z APCI 330 [M+H]⁺

Microanalysis: C₁₃H₁₀Cl₃N₃O requires: C, 47.23; H, 3.05; N, 12.71. foundC, 47.15; H, 3.18; N, 12.55.

EXAMPLE 2 6-Amino-5-(2,3,5-trichloro-phenyl)-pyridine-2-carboxylic acid(2-piperidin-1-yl-ethyl)-amide

A solution of 1-(2-aminoethyl)piperidine (0.60 g, 4.71 mmol) intetrahydrofuran (2.4 mL) was added to a suspension of the product ofpreparation 3 (0.16 g, 0.47 mmol) in methanol (4 mL) and tetrahydrofuran(2 mL) and the mixture was heated at 50° C. for 72 hours. The reactionmixture was then concentrated in vacuo and the residue was purified bycolumn chromatography on silica gel, eluting withdichloromethane:methanol, 90:10 to afford the title compound as a yellowsolid in 92% yield, 0.19 g.

¹H NMR (400 MHz, CD₃OD) δ: 1.45-1.54 (m, 2H), 1.60-1.69 (m, 4H),2.53-2.66 (m, 6H), 3.58 (t, 2H), 7.33 (d, 1H), 7.42 (dd, 2H), 7.69 (d,1H) LRMS: m/z APCI 427 [M+H]⁺

Microanalysis: C₁₉H₂₁Cl₃N₄O 0.5H₂O requires: C, 52.25; H, 5.08; N,12.83. found C, 52.52; H, 4.96; N, 12.87.

EXAMPLE 3 6-Amino-5-(2,3,5-trichloro-phenyl)-pyridine-2-carboxylic acid(3-pyrrolidin-1-yl-propyl)-amide

The title compound was prepared from the product of preparation 3 and1-(3-aminopropyl)pyrrolidine, using a method analogous to that ofexample 2. The crude compound was purified by column chromatography onsilica gel, eluting with dichloromethane:methanol:0.88 ammonia, 90:10:1,followed by trituration with diethyl ether to afford the desired productin 60% yield, 61.5 mg.

¹H NMR (400 MHz, CD₃OD) δ: 1.81-1.92 (m, 6H), 2.65-2.75 (m, 6H),3.44-3.50 (m, 2H), 7.33 (d, 1H), 7.42 (dd, 2H), 7.70 (d, 1H) LRMS: m/zAPCI 427 [M+H]⁺ Microanalysis: C₁₉H₂₁Cl₃N₄O 0.5H₂O requires: C, 52.25;H, 5.08; N, 12.83. found C, 52.02; H, 4.86; N, 12.61.

EXAMPLE 4 6-Amino-5-(2,3,5-trichloro-phenyl)-pyridine-2-carboxylic acid(3-morpholin-4-yl-propyl)-amide

A solution of 2-(4-morpholino)propylamine (87 mg, 0.6 mmol) in methanol(0.5 mL) was added to a solution of the product of preparation 3 (20 mg,0.06 mmol) in tetrahydrofuran (0.5 mL) and the mixture was stirred atroom temperature for 72 hours. The reaction mixture was concentrated invacuo and the residue was purified by column chromatography on silicagel, eluting with dichloromethane:methanol, 90:10, to afford the titlecompound in 71% yield, 19 mg.

¹H NMR (400 MHz, CD₃OD) δ: 1.80-1.88 (m, 2H), 2.43-2.53 (m, 6H), 3.45(m, 2H), 3.65 (m, 4H), 7.33 (d, 1H), 7.42 (dd, 2H), 7.70 (d, 1H) LRMS:m/z APCI 443 [M+H]⁺

EXAMPLE 5 6-Amino-5-(2,3,5-trichloro-phenyl)-pyridine-2-carboxylic acid(2-pyrrolidin-1-yl-ethyl)-amide

A mixture of the product of preparation 3 (20 mg, 0.06 mmol) and1-(2-aminoethyl)pyrrolidine (69 mg, 0.6 mmol) in tetrahydrofuran (0.5mL) and methanol (0.5 mL) was placed in a microwave tube and heated in amicrowave for 30 minutes at 130° C. The mixture was then stirred at roomtemperature for 72 hours before the solvent was evaporated under reducedpressure. Purification by column chromatography on silica gel, elutingwith dichloromethane:methanol, 90:10, afforded the title compound in 88%yield, 22 mg.

¹H NMR (400 MHz, CD₃OD) δ: 1.80-1.90 (m, 4H), 2.65 (m, 4H), 2.75 (t,2H), 3.59 (m, 2H), 7.34 (d, 1H), 7.42 (dd, 2H), 7.69 (d, 1H) LRMS: m/zAPCI 413 [M+H]⁺

EXAMPLE 6 6-Amino-5-(2,3,5-trichloro-phenyl)-pyridine-2-carboxylic acid(3-imidazol-1-yl-propyl)-amide

1-(3-Aminopropyl)imidazole (0.28 mL, 2.42 mmol) was added to a solutionof the product of preparation 3 (122.6 mg, 0.37 mmol) in tetrahydrofuran(4 mL) and methanol (0.5 mL) and the mixture was heated at 65° C. for 18hours and at 75° C. for 72 hours. The reaction mixture was thenconcentrated in vacuo and purified by column chromatography on silicagel, eluting with dichloromethane:methanol:0.88 ammonia, 90:10:0.1,followed by trituration in dichloromethane/diethyl ether to afford thetitle compound as a white solid in 70% yield, 110 mg.

¹H NMR (400 MHz, CD₃OD) δ: 2.11 (m, 2H), 3.42 (m, 2H), 4.12 (m, 2H),6.97 (s, 1H), 7.20 (s, 1H), 7.34 (d, 1H), 7.43 (dd, 2H), 7.69 (d, 1H),7.72 (d, 1H) LRMS: m/z APCI 424 [M+H]⁺ Microanalysis: C₁₈H₁₆Cl₃N₅O0.25H₂O requires: C, 50.37; H, 3.87; N, 16.32. found C, 50.36; H, 3.84;N, 16.15.

Preparation 1 N-(3-Bromo-6-methyl-pyridin-2-yl)-acetamide

Acetic anhydride (21 mL, 223 mmol) was added to a solution of2-amino-3-bromo-6-picoline (10 g, 53.46 mmol) in dioxan (50 mL) and themixture was stirred at 50° C. for 18 hours. The solvent was thenevaporated under reduced pressure and the residue was diluted withsaturated sodium hydrogen carbonate solution (150 mL). The precipitatewas filtered off, washed with water and re-dissolved in dichloromethane,and the filtrate was neutralised to pH7 with saturated sodium hydrogencarbonate solution and extracted with dichloromethane (3×100 mL). Theorganic solutions were combined, washed with water, dried over magnesiumsulfate and concentrated in vacuo to give a white solid. Purification ofthe solid by column chromatography on silica gel, eluting with ethylacetate:heptane, 75:25, afforded the title compound as a white solid in75% yield, 9.2 g.

¹H NMR (400 MHz, CD₃OD) δ: 2.17 (s, 3H), 2.49 (s, 3H), 7.09 (d, 1H),7.94 (d, 1H)

LRMS: m/z APCI 231 [M+H]⁺ Microanalysis: C₈H₉BrN₂O requires: C, 41.95;H, 3.96; N, 12.23. found C, 41.92; H, 3.91, N, 12.16.

Preparation 2 6-Amino-5-bromo-pyridine-2-carboxylic acid methyl ester

Potassium permanganate (9.77 g, 61.81 mmol) was added portionwise to asolution of the product of preparation 1 (4.8 g, 20.95 mmol) in water(100 mL) and pyridine (8 drops) and the mixture was heated at 75° C. for18 hours. Further potassium permanganate (3.31 g, 61.81 mmol) was thenadded to the mixture and stirring continued at 75° C. for 18 hours. Thereaction mixture was then filtered through Celite® and the filtrate waswashed with ethyl acetate (6×50 mL). The aqueous solution wasconcentrated in vacuo to give a pale yellow solid that was azeotropedwith toluene (5×50 mL) at 50° C. to afford the crude potassium salt asan intermediate. The intermediate was then dissolved in methanol (400mL) and heated under reflux. Concentrated sulphuric acid (5 mL) wasadded to the mixture and heating continued for 2 days. The solvent wasthen evaporated under reduced pressure and the residue was basified topH8 with a saturated sodium hydrogen carbonate solution (150 mL) andextracted with dichloromethane (3×50 mL). The combined organic solutionswere dried over magnesium sulfate and concentrated in vacuo to affordthe title compound as a pale yellow solid in 34% yield, 1.65 g.

¹H NMR (400 MHz, CD₃OD) δ: 3.90 (s, 3H), 7.25 (d, 1H), 7.88 (d, 1H)LRMS: m/z ES 233 [M+H]⁺ Microanalysis: C₇H₇BrN₂O₂ requires: C, 36.39; H,3.05; N, 12.12. found C, 36.24; H, 3.08; N, 11.94.

Preparation 3 6-Amino-5-(2,3,5-trichloro-phenyl)-pyridine-2-carboxylicacid methyl ester

A solution of bis(tri-tert-butylphosphine)palladium(0) (9.3 mg, 0.18mmol) in tetrahydrofuran (2 mL) was added to a mixture of the product ofpreparation 2 (0.21 g, 0.90 mmol), potassium fluoride (0.17 g, 2.86mmol), 2,3,5-trichlorobenzeneboronic acid (0.21 g, 0.95 mmol) andtris(dibenzylideneacetone)dipalladium(0) (9.3 mg, cat.) intetrahydrofuran (4 mL) and the reaction mixture was stirred undernitrogen for 18 hours at room temperature. The mixture was then dilutedwith diethyl ether, filtered through Arbocel® and washed with furtherdiethyl ether. The filtrate was concentrated in vacuo and purified bycolumn chromatography on silica gel, eluting with heptane:ethyl acetate,66:33, to afford the title compound as a white solid in 83% yield, 0.25g.

¹H NMR (400 MHz, CD₃OD) δ: 3.94 (s, 3H), 7.35 (d, 1H), 7.48 (m, 2H),7.70 (d, 1H)

LRMS: m/z APCI 331 [M+H]⁺ Microanalysis: C₁₃H₉Cl₃N₂O₂ requires: C,47.09; H, 2.74; N, 8.45. found C, 47.05; H, 2.80; N, 8.51.

Preparation 4 6-Amino-5-bromo-pyridine-2-carboxylic acid methylamide

Methylamine (2M, in tetrahydrofuran, 36.8 mL, 73.64 mmol) was added to asuspension of the product of preparation 2 (1.70 g, 7.36 mmol) inmethanol (10 mL) and the mixture was stirred for 18 hours at roomtemperature. The reaction mixture was then concentrated in vacuo and theresidue was purified by column chromatography on silica gel, elutingwith ethyl acetate:heptane, 75:25, to afford the title compound as asolid in 96% yield, 1.63 g.

¹H NMR (400 MHz, CD₃OD) δ: 2.90 (s, 3H), 7.20 (d, 1H), 7.82 (d, 1H)LRMS: m/z APCI 231 [M+H]⁺ Microanalysis: C₇H_(B)BrN₃O requires: C,36.55; H, 3.50; N, 18.26. found C, 36.50; H, 3.47; N, 18.12.

¹H Nuclear magnetic resonance (NMR) spectra were in all cases consistentwith the proposed structures. Characteristic chemical shifts (6) aregiven in parts-per-million downfield from tetramethylsilane usingconventional abbreviations for designation of major peaks: e.g. s,singlet; d, doublet; t, triplet; q, quartet; m, multiplet; br, broad.The mass spectra (m/z) were recorded using either electrosprayionisation (ESI) or atmospheric pressure chemical ionisation (APCI). Thefollowing abbreviations have been used for common solvents: CD₃OD,deuteromethanol; THF, tetrahydrofuran. ‘Ammonia’ refers to aconcentrated solution of ammonia in water possessing a specific gravityof 0.88.

Microwave radiation was provided using the Emrys Creator or the EmrysLiberator, both supplied by Personal Chemistry Ltd. The power range is15-300 W at 2.45 GHz. The actual power supplied varies during the courseof the reaction to maintain a constant temperature.

All the compounds of the Examples have been tested in the assaydescribed on pages 34-38 and found to have an affinity for the Na_(V1.8)channel of less than 10 μM. In particular, Examples 1 and 7 had bindingaffinities of 2.04 and 5.48 μM respectively.

All the compounds of the Examples have been found to have at least a2-fold selectivity for the Na_(V1.8) channel over the TTX-S sodiumchannels, using the test method described on page 38.

1. A compound of the formula:

or a pharmaceutically acceptable salt or solvate thereof, wherein: R¹ is(C₁-C₆)alkyl optionally substituted with Het¹, Het² or(C₃-C₇)cycloalkyl, wherein said Het¹, Het² and (C₃-C₇)cycloalkyl areoptionally substituted on a ring carbon atom by one or more substituentseach independently selected from (C₁-C₄)alkyl, (C₁-C₄)alkoxy andhalo(C₁-C₄)alkyl; each R² is independently selected from fluoro, chloro,bromo and iodo; n is 1, 2 or 3; Het¹ is a 5- or 6-membered saturated orpartially unsaturated heterocyclic group comprising one or twoheteroatom ring members each independently selected from nitrogen,oxygen and sulphur, said ring nitrogen atom optionally bearing a(C₁-C₄)alkyl substituent and said ring sulphur atom optionally bearing 1or 2 oxygen atoms; and Het² is a 5- or 6-membered heteroaryl groupcomprising either (a) from 1 to 4 nitrogen atoms or (b) one oxygen orone sulphur atom and 0, 1 or 2 nitrogen atoms.
 2. A compound accordingto claim 1, wherein each R² is chloro.
 3. A compound according to claim1 or claim 2, wherein n is
 3. 4. A compound according to claim 3,wherein the R² groups are in the 2, 3 and 5-positions on the phenyl,ring.
 5. A compound according to any one of claims 1 to 4, wherein R¹ is(C₁-C₆)alkyl, optionally substituted with piperidinyl, imidazolyl,morpholinyl, piperazinyl or pyrrolidinyl.
 6. A pharmaceuticalcomposition including a compound of the formula (I) or apharmaceutically acceptable salt or solvate thereof, according to claim1, together with one or more pharmaceutically acceptable excipients.